Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Wildland Resources

Department name when degree awarded

Range Science

Committee Chair(s)

Don D. Dwyer


Don D. Dwyer


Two common use grazing trials were conducted during two summer grazing seasons (1978-1979) on a typical shrubby grassland site on the Kolab Terrace, about 20 miles (32 km) southeast of Cedar City, Utah, at an elevation of about 8500 feet (2600 m). Two animal units of ewes with lambs, or cows with calves, or both were stocked in each of six, one-acre (0.39 ha) pastures. A five to one substitution ratio provided two single-species and one mixed (five ewes with lambs and one cow with calf) livestock treatments replicated twice. The pastures were grazed for nine days during which time two major experiments were performed.

In the first experiment, livestock forage preferences were quantified so that precise single-species and common use grazing capacities could be determined. Disappearance of the current season's production of herbaceous vegetation was measured using clipped plots (a modified, "paired plot" procedure) and step-point transects (with grazed plant heights and percent of plants grazed). A predictive regression (r2=0.90) of the stem diameters of snowberry (Symphoricarpos vaccinioides), the dominant shrub on the site, with the cubed roots of the combined dry matter of its stems plus leaves was used for estimating browse utilization. Rates of utilization in kilograms per day of the grass, forb and shrub components were computed from the data in terms of increasing herbage use (disappearance). Simple stocking rate relationships, using the rates and proper use considerations, were employed to predict sheep to cattle substitution ratios and optimum mixes of the two species for sites similar to that studied. Results indicated a decrease in the sub-situation ratio as the relative snowberry density of sites decreased because of the higher rate of browse use by sheep. Proper use of the shrub constrained sheep grazing capacity under these conditions causing a significant, but small, gain in total grazing capacity under common use. Levels of utilization of selected forage components recorded in mixed livestock treatments were significantly different from levels predicted for mixed herds based on single-species treatments. This indicated an effect of mixing cattle with sheep, a social facilitation of forage preferences.

The second experiment, studies of sheep and cattle behavior, provided additional information about the effects of common use on livestock. The pasture layout was such that the behavior of sheep, cattle and mixed groups could be observed in both an isolated situation and in pastures with common fences. Locations and activities for all animals within each pasture were mapped every hour during four days of each grazing trial. Average distances between animals, among groups of animals and between them and key pasture features (fencelines, watering areas) and associated animal activities were determined by livestock species, hour of day, trial day (herbage quantity) and pasture arrangement. Cattle influenced the morning distribution and activities of sheep in isolated pastures. As the trials progressed, and herbaceous forage became limiting, browsing activity increased in both sheep and cattle. No major differences in distribution or activity patterns were recorded which clearly distinguished mothers from offspring of either livestock species.

The research approach (small scale, intense data collection) presented was appropriate, informative and economic for studying this site and should apply as well to other sites. A discussion of the study methodology was included.



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